On Wed, Dec 20, 2017 at 02:18:59PM +0530, Viresh Kumar wrote: > On 20-12-17, 09:31, Peter Zijlstra wrote: > What about this case: A CFS task is running currently and an RT task > is enqueued. > > - Is it always the case that the CFS task is preempted immediately and > the CPU is given to RT task ? I was talking to Vincent earlier and > he told me that for certain configurations the CFS task may keep > running until the next tick. > > - What if the CFS task has disabled preemption ? > > - More corner cases like this ?
If there is a runnable RT task we'll schedule to it ASAP. This means for: CONFIG_PREEMPT=y either immediately or when next preempt_enable() hits a 0 preempt_count. CONFIG_PREEMPT=n on any next kernel preemption point or when returning to userspace. But this is not something we should worry about.
